This invention relates generally to the field of injection molding plastic articles, such as blowable plastic parisons, around a set of cylindrical core pins, cooling the articles while on the core pins, and then stripping the molded articles from the core pins for subsequent processing.
The art of forming bottles and containers by blow molding has advanced to the stage where several thousands of such articles can be formed each hour. This necessarily requires that the blowable parisons from which the articles are blown be formed rapidly and inexpensively, either by extrusion or injection molding techniques. In injection molding processes, it therefore becomes important to reduce the overall cycle time and to reduce the tooling expenses. Additionally, it is desirable in many situations that the parisons have a thickness profile to optimize material usage.
The prior injection molding machines have not provided these overall desirable features. For example, one prior art injection molding technique utilizes horizontally reciprocable molds including core pins which are telescopically inserted into an elongated horizontal mold cavity. This arrangement exhibits several shortcomings, including: first, difficulty in molding tapered parisons with controlled varying thicknesses; second, relatively high cycle times; and third, expensive tooling, for example, because cam-operated mold sections are needed to form the threaded finish.
A further difficulty has been encountered in high speed operation of such machines, namely, that stripping of the injection molded parisons from the supporting core pins has very often resulted in damage to the neck finish portion of such parison. This is believed due to the fact that most stripping operations have applied the stripping forces to the threads and/or a relatively wide flange that commonly appears at the bottom portion of a bottle neck so that the force exerted on the extreme end portions of the parison neck are primarily tensile and, as is well known, heated thermoplastic material is very weak in tension and readily subject to cracking.